15^ DISPERSAL DURING [Chap. Xll. 



inorganic, that, within a very recent geological period, 

 central Europe and North America suffered under an 

 arctic climate. The ruins of a house burnt by Are do 

 not tell their tale more plainly than do the mountains 

 of Scotland and Wales, with their scored flanks, pol- 

 ished surfaces, and perched boulders, of the icy streams 

 with which their valleys were lately filled. So greatly 

 has the climate of Europe changed, that in Northern 

 Italy, gigantic moraines, left by old glaciers, are now 

 clothed by the vine and maize. Throughout a large 

 part of the United States, erratic boulders and scored 

 rocks plainly reveal a former cold period. 



The former influence of the glacial climate on the 

 distribution of the inhabitants of Europe, as explained 

 by Edward Forbes, is substantially as follows. But we 

 shall follow the changes more readily, by supposing a 

 new glacial period slowly to come on, and then pass 

 away, as formerly occurred. As the cold came on, and 

 as each more southern zone became fitted for the in- 

 habitants of the north, these would take the places of 

 the former inhabitants of the temperate regions. The 

 latter, at the same time, would travel further and fur- 

 ther southward, unless they were stopped by barriers, 

 in which case they would perish. The mountains 

 would become covered with snow and ice, and their for- 

 mer Alpine inhabitants would descend to the plains. 

 By the time that the cold had reached its maximum, we 

 should have an arctic fauna and flora, covering the 

 central parts of Europe, as far south as the Alps and 

 Pyrenees, and even stretching into Spain. The now 

 temperate regions of the United States would likewise 

 be covered by arctic plants and animals and these would 

 be nearly the same with those of Europe; for the 



